Diseases of epithelial cells are the single most common cause of morbidity and mortality of humans. Foremost among these diseases is cancer. Other diseases which are epithelial in origin include, for example, blistering disease (e.g., epidermolytic hyperkeratosis, and Dowling-Meara disease) proliferative disease (e.g., psoriasis, epidermal lysis, and Bulosa simplex) and Ichthyosis disease (e.g. Ichthyosis bullosa Simens, and recessive X-linked ichthyosis). The location of the epithelium as the lining of tissue surfaces in the body places it at a particularly high risk for repeated damage from a variety of agents in the environment. For example, most of the prevalent epithelial cancers (e.g., cancer of the lung, breast, colon, liver, cervix, etc.) are associated with exposure to carcinogens such as cigarette smoke, hydrocarbons in grilled foods, toxic molds, and infection with genital DNA tumor viruses.
The evaluation of candidate therapeutics directed at the treatment of epithelial disease has traditionally focused on animal models in which the animal is repeatedly exposed to one or a combination of chemicals. For example, models for cancer development and treatment rely on administration of carcinogenic and co-carcinogenic compounds. However, one drawback to such a model is that animals treated with chemicals exhibit a multitude of genetic and metabolic alterations. The multiplicity of genetic and metabolic changes makes it difficult to determine which of this multitude of changes is causally related to the resulting disease state, and hence makes it also difficult, if not impossible, to identify candidate therapeutics which target only relevant genetic and/or metabolic lesions. The further problems of unpredictability and variability of genetic and metabolic changes in response to chemical treatment make such animals poor models for the evaluation of therapeutics.
More recently, trangenic animals which harbor known genetic alterations and which express epithelial disease have been used. In particular, transgenic animal models which develop cancer and in which selected genes are expressed in epithelial cells in general (e.g., U.S. Pat. No. 5,550,316; Griep et al. (1994) Proc. Soc. Exp. Biol. Med. 206:24-34; Kondoh et al. (1995) Intervirology 38:181-186; Yang et al. (1995) Am J. Pathol. 147:68-78; Greenhalgh et al. (1994) Cell Growth Differ. 5:667-675; Tinsley et al. (1992) J. Gen. Virol. 73:1251-1260) have been described.
For example, the involvement of human papillomavirus (HPV) in cancer development has been investigated in model transgenic animals. Mice transgenic with HPV16 oncogenes express a number of malignancies (Table 1).
TABLE 1 Transgenic Animals Containing HPV-16-Oncogenes Sites of mRNA or Promoter Gene Protein Expression Major Phenotype References Human keratin 14 HPV-16 E7 Epidermis; hair Epidermal hyperplasia in Herber et al. follicles; skin, mouth palate, (1996) J. Virol. sebaceous glands. esophagus, forestomach, 70:1873-1881 and exocervix; skin rumor. Human .beta.-actin HPV-16 E6 Epidermis; cervix; Epidermal hyperplasia; Arbeit et al. and E7 vagina. cervical dysplasia; vaginal (1996) Proc. Natl. and cervical dysplasia and Acad. Sci. USA carcinoma in situ (17-.beta.- 93:2930-2935. estradiol). Bovine HPV-16 E7 Thyroid. Differentiated goiters; Ledent et al. thyroglobulin invasive undifferentiated (1995) Oncogene goiters. 10:1789-1797 .alpha.A-crystallin HPV-16 E6 Skin; eyes. Squamous cell carcinoma; Frazer et al. and E7 lenticular tumor. (1995) Cancer Res. 55:2635- 2639. MMTV HPV-16 E6 Cervix; vagina; Cervical and vaginal Sasagawa et al. and E7 salivary gland. dysplasia and hyperplasia; (1994) J. Gen. salivary gland carcinoma; Virol. 75:3057- lymphoma; skin 3065. histiocytoma. Bovine Keratin 6 HPV-16 Tongue; stomach; Metastatic stomach tumors. Searle et al. early female (1994) J. Gen. region reproductive tract; Virol. 75:1125- tail skin. 1137. Human Keratin HPV-16 Skin. Ear epidermal hyperplasia Arbeit et al. 14 early and dysplasia; facial (1994) J. Virol. region epidermal hyperplasia and 68:4358-4368. papillamatosis; anal papilioma; truncal ulcers, diffuse epidermal hyperplasia; cataracts; lenticular hyperplasia. Human keratin 14 HPV-16 B6 Skin. Ear epidermal hyperplasia Arbeit et al. and E7 and dysplasia; facial (1994) epiedermal hyperplasia and WO/95/33820; papillomatosis; anal Arbeit et al, papillomas, truncal ulcers; (1994) WO cataracts; cervico-vaginal 95/33826. carinoma (17-.beta.-estradiol). Human .alpha.-actin HPV-16 E6 Neuroepithelial Neuroepithelial carcinoma. Arbeit et al. and E7. tumors (1993) Am. J. Pathol. 142:1187- 97. .alpha.A-crystallin HPV-16 E6 Ocular lens; skin. Bilateral microphthalmia Lambert et al. and E7 and lens tumor; skin (1993) Proc. Natl. preneoplastic lesion and Acad, Sci. USA carcinoma. 90:5583-5587. .alpha.A-crystallin HPV-16 E6 Ocular lens; eye Lens tumor. Griep et al. (1993) and E7 without lens; brain, J. Virol. 67: 1373- intestine, tail. 84. MMTV-LTR HPV-16 E6 Testicular tumor; Testicular tumor Kondoh et al. and E7 submandibular (seminoma). (1991) J. Virol. gland. 65:3335-3339.
While there exist transgenic animals which develop epithelial cell disease in general, and neoplastic and/or preneoplastic lesions in particular, there is no transgenic model for some epithelial diseases (e.g., blistering disease, proliferative disease, and Ichthyosis disease) or for certain cancers (e.g., colon cancer, anal cancer, etc.). Furthermore, because the development of a single cancer phenotype may be caused by more than one genetic alteration, even those cancers for which there is available a transgenic animal model having a defined genetic lesion, such a single transgenic animal model is potentially of limited use in comprehensive screening of therapeutics. This is because a compound which is not therapeutic in a transgenic animal that has a particular genetic alteration, may nevertheless be therapeutic in a transgenic animal which develops the same disease as a result of a different genetic alteration.
Thus, there is a need for a better model of epithelial cell disease. This model should be amenable to identifying therapeutic compounds.